Boosting generation of reactive oxygen and chlorine species on TNT photoanode and Ni/graphite fiber cathode towards efficient oxidation of ammonia wastewater

Sen Lu; Xuechuan Li; Yunkai Liao; Zhenghua Zhang; Haijian Luo; Guan Zhang

doi:10.1016/j.chemosphere.2022.137363

Boosting generation of reactive oxygen and chlorine species on TNT photoanode and Ni/graphite fiber cathode towards efficient oxidation of ammonia wastewater

Chemosphere. 2023 Feb:313:137363. doi: 10.1016/j.chemosphere.2022.137363. Epub 2022 Nov 21.

Authors

Sen Lu¹, Xuechuan Li¹, Yunkai Liao¹, Zhenghua Zhang², Haijian Luo³, Guan Zhang⁴

Affiliations

¹ State Key Laboratory of Urban Water Resource and Environment, Shenzhen Key Laboratory of Organic Pollution Prevention and Control, School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, Shenzhen, 518055, PR China.
² Institute of Environmental Engineering & Nano-Technology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, PR China.
³ Education Center of Experiments and Innovations, Harbin Institute of Technology, Shenzhen, Shenzhen, 518055, PR China. Electronic address: luohaijian@hit.edu.cn.
⁴ State Key Laboratory of Urban Water Resource and Environment, Shenzhen Key Laboratory of Organic Pollution Prevention and Control, School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, Shenzhen, 518055, PR China. Electronic address: zhangguan@hit.edu.cn.

PMID: 36423725
DOI: 10.1016/j.chemosphere.2022.137363

Abstract

Photoelectrocatalytic (PEC) process combining the merits of photocatalysis and electrocatalysis is considered as a promising ammonia oxidation technology for water treatment. However, some key issues, such as the limited in situ generation of oxidants on photoanode, slow mass transfer problem and generation of nitrate/nitrite by-products hinder the further application of PEC process in the treatment of ammonia pollutant. In this study, the graphite felt (GF) cathodes modified by different transition metals (Ni, Fe, Mn, Co, Cu) were screened by physicochemical and photoelectrochemical characterizations. The results show that the Ni-GF cathode with more Ni⁰ uniformly distributed on the GF surface had the best electrocatalytic activity to generate H₂O₂. The PEC system composed of 10.0 wt% Ni-GF cathode and optimized titania nanotubes (TNTs) photoanode selectively converted about 96.1% ammonia to N₂ within 90 min. Compared with the single TNTs photoanode system, the ammonia oxidation reaction rate constant of the synergistic PEC oxidation system was increased by about two times, which demonstrated the role of the oxidants simultaneously generated on both anode and cathode. The in situ generated reactive oxygen-based oxidants and chlorine-based oxidants interacted together, and ClO• acted a leading role in the ammonia oxidation which were confirmed by quenching and probe experiments. In addition, the contributions of •OH and ClO• were significantly improved in the synergistic PEC oxidation system, compared with the single TNTs photoanode system. Furthermore, the nitrate by-products generated by the ammonia oxidation were further reduced on the Ni-GF cathode. The large amount of active chlorine and active oxygen generated on the electrode diffused into the bulk, effectively overcoming the mass transfer limitation of direct oxidation. Therefore, the developed TNTs photoanode/Ni-GF cathode system can continuously and efficiently convert ammonia to N₂ without the formation of nitrate/nitrite by-products.

Keywords: Ammonia removal; Chlorine-based radicals; Graphite cathode; Photoelectrocatalytic oxidation; Transition metals.

MeSH terms

Ammonia
Chlorine*
Electrodes
Graphite*
Hydrogen Peroxide
Nitrates
Nitrites
Oxidants
Oxygen
Wastewater

Substances

Chlorine
Wastewater
Ammonia
Graphite
Oxygen
Hydrogen Peroxide
Nitrates
Nitrites
Oxidants